Multicolor storage tube



Oct. 27, 1959 s. 1'. SMITH MULTICOLOR STORAGE TUBE Filed Sept. 27, 1955 2 Sheets-Sheet 1 W 5 m7 NY ni MN m .Fza 3 A TZOEA/E Y Oct. 27, 1959 s. 'r. SMITH MULTICOLOR STORAGE TUBE 2 Sheets-Shea}. 2

Filed Sept. 27, 1955 ATHENEVY 2,910,617 w MULTICOLOR STORAGE I Sidney T. Smith, -Pacit iclPalisades ,caliig assignor to Hughes'Aircraft Company, Culver City, Calif., a. corporationof Delaware j 'w 3 Application September 27, 1955, Serial No. 536,875

2 Claims. Cl. 315-12 This invention relates to direct-viewing storage tubes,

and more particularly to a long-persistence three-color indicator tube of the cathode-ray type capable of producing a visual half-tone presentation of good color purity.

The direct-viewing storage tube of the present invention comprises "three electron guns for producing, re-

spectively, three electron beams which are-scanned over ited States Patent" set of three apertures of the storage screen which are in alignmentwith three adjacent diflferent colored phosphor dots on the viewing screen. The placement of--the' apertures in the storage screen relative to the openings in the shadow mask is such that each electron beam,

' upon penetrating through an opening in the shadow mask,

is incident on the storage surface surrounding only the aperture in the storage screen inalignment with its asso-- ciated. color of phosphor dot on the viewing screen. A color presentation is then produced by directing flood electrons through the shadow mask and thence through the apertures in .the storage screen in proportion to the charge'on the surrounding storage surface to the corresponding phosphor dots on the viewing screen.

One of the problems encountered in: present day multicolor direct-viewing storage tubes of this type is that of maintaining color purity. In order to achieve color purity in prior art devices, it was found'neces sa'ry to employ a storage screen having at least 5 to 10 interstices per color dot on the viewing screen. For a picture having normal resolution, this necessitated the useof a storage screen having, for example, 500 meshes per inch. A

storage screen having interstices this small, however, re-

duced the electric field penetration from the viewing screen to the extent that'no half-tones could be reproduced. Thus, it is apparent that color purity considerations dictated the use of a fine mesh storage screen, while reproduction of half-tones dictated the use of a coarse storage screen.

In accordance with the present invention, the above conflicting considerations are eliminated by employing a storage screen having a single circular aperture in alignment with each phosphor dot on the viewing screen. Further, in order to maintain color purity, the storage surface is symmetrically disposed about each aperture of the storage screen so as not to impart anytransverse velocity to the flood electrons when passing through the storage screen. It has been found that such a structure in that each color dot has its individually aligned beam Patented Oct. 27, 1959 2 cially important in large-diameter curved-screen construction.

It is therefore an object of the invention to'provide an improved multicolor direct-viewing storage tube.

Another object of the invention is to provide'a directviewing storage tube adapted toproduce a color presentation having both color purityand half-tones.

A :fur't-herobject 'ofthe invention is to providea three electron gun, three-color, direct-viewing storagel tube adapted for use with-conventional" systems to produce a television picture incolor.

The novel features whih are believed to be characteristic of the invention, Both as to its organization and method of operation, together with further objects and advantages thereofgwill be better understood from the following description considered in connection with the accompanying drawings which 'an embodiment of the invention is illustrated by way of example. It is to be expressly understood, however,- that the drawings are for the purpose or illustration and description only, and are not intended as a definition of the limits of the invention. V v

Fig. 1 is a; longitudinalsectional view of a directviewing storage tube embodying the present invention;

Fig. 2 is a greatly enlarged view of a portionof the viewing screen in the device of Fig. I;

Figs: 3 and 4'are greatly enlarged planpand' crosssectional'views, respectively, of the storage screen in the device of Fig.- 1;

Figs. '5 andr6 are greatlyenlarged' plan andcrosssectional views, respectively, of the shadow mask in the device of Fig. 1.; r

Fig; v7 is a greatly enlarged plan view showing the manner inwhich the phosphor dots of the viewing screen, the apertures in the storage screen, and the openings in the shadow mask are aligned at a central portion of the screens in the device'of Fig.1; and

Fig. 8 is a schematic. view'in'p'erspective illustrating the mannerin which thethreeelectro'n beams of'the electron guns in the device of 'Fig; 1 pass through a given opening in the shadow mask and impinge on the storage surface surrounding selected apertures in the storage surface.

Reference will: be. madefirst to Fig. 1 for a general description of an illustrative embodiment of the multicolor direct-viewing: storage device of the present invention. The device comprises an evacuated bulbous envelope 10 having a substantially flat portion 11 and a neck portion 12 at opposite extremities. thereof. For the purpose of explanation, it will be assumed that a presentation having three primary colors is to be produced. Accordingly, the neck portion 12 of the envelope 10 is adapted to house electron guns 14, 16' and 18. These electron guns are'symmetrically disposed about the longitudinal-axis through the neck portion 12 and are equal in number to the aforementioned number of primary and, lastly, greater strength and rigidity whichv is especolors. The three electron guns 14 16 and18 are conventional and produce three electron-beams which are represented schematically'in' the right half of the envelope 10; as viewed in the drawing, with their angular relationships greatly exaggerated for purposes of illustration, by the dashed lines 20, 22 and 24, respectively.

Each of'the electron guns 14, 16, 18 has impressed thereon avideocolor signal provided by a video source 26 in a manner to intensity modulate the electron beams 20, 22 and 24,"respectively'.

Adjacent the flat portion 11 of. the envelope 10 there is disposed, in the order named, aviewing screen 28; a storage screen30, and, a' shadow. mask 32. In addition, amagnetic convergence coil 34' and magnetic electron beam deflecting yokes 36, 38' are disposedabout the outr 3 side of the neck portion 11 of envelope for converging the electron beams together in the plane of the shadow mask 32 and for simultaneously directing the electron beams towards selectedelemental areas of the storage screen 30, respectively. It is realized, of course, that the angles between the beams 20, 22, 24 and the spacing between the shadow mask 32 and the storage screen 30 as compared withJthe length of the tube are exaggerated for better illustration of the operation of the tube. Also, an equipotential region is provided between the electron guns 14, 16, 18 and the shadow, mask 32 by means of a conductive coating 40 disposed about the inner surface of the envelope 10 therebetween. Lastly, an annular flood gun 42 for providing a sourceof flood electrons is disposed about the paths of the electron beams at the extremity of envelope 10 adjacent the junction with the neck portion 12. l More particularly, as indicated in Fig. 1, the viewing screen 28 is disposed directly on the inner surface of the flat portion 11 of evacuated envelope 10. The viewing screen 28 comprises a transparent conductive coating 50 on top of which is disposed a phosphor dot viewing screen 52, as shown in Fig. 2. An aluminized layer over the phosphor dots could be used in lieu of the conductive coating. In the event that it is desired to reproduce the true colors;of.a picture, the phosphor dots of the viewing screen 28 are composed of three primary colors such as, for example, red, blue and green. These phosphor dots may have a diameter of the order of 0.0136 inch and are arranged so that the perimeter of a. dot of any one color is in contact with the perimeter of 'dots of the remaining two color dots disposed alternately as illustrated in the figure. Thus, as can be seen in this figure, 5

any group of three dots in mutual contact with each other includes one each of the primary color dots.

Referring to Figs. 1, 3 and 4, the storage screen 30 is disposed adjacent to and coextensive with the viewing screen 28 and may comprise, for example, a thin. sheet 54 of metal of the order of 0.004" thick which has apertures 56 of a diameter of the order of 0.004" in alignment with each phosphor dot'of the viewing screen 28. It has been found that an alloy of 70% copper and 30% nickel is a suitable metal out of which to fabricate the sheet 54 of the storage screen. A thin layer 58 of dielectric material having secondary. electron emission characteristics such as, for example, magnesium fluoride is evaporated on the side of themetallic sheet 54 facing the electron guns 14, 16 and 18. This layer 58 is of a uniform thickness of the order of two microns.

When evaporating the layer 58 of dielectric material on the one side of the metallic sheet 54, it is essential that no particles of dielectric material be deposited within the apertures 56 in an unsymmetrical way. The reason for this is that, in order to maintain color purity, it is necessary that no transverse velocity be imparted to the flood electrons in traversing through the apertures 56 to the phosphor dots on the viewing screen 28. In

operation, any particles of dielectric deposited within the apertures 56 may accumulate erroneous charges from the viewing screen 28 or from the electron beams 20, 22, 24 and thus'impart sufficient transverse components of velocity to the flood electrons to cause them to implnge on an adjacent phosphor dot. In addition it may be desirable to leave a small symmetrical portion of the metallic plate 54 about each of the apertures 56 exposed so as to increase the range potentialsfover which halftone signals may be stored. The manner in which a screen of this type may be fabricated is taught in a copending application for patent, Serial No. 519,384, filed June 30, 1955, now Patent No[ 2,858,463, entitled Storage Screen for Direct-Viewing Storage Tube, by Sidney T. Smith and Nobuo I. 'Koda and assigned to the same assignee as is the present application. As taught in the above application for. patent, the metallic plate 54 is 4 coated with a layer of photoresist, one side of the coated plate 54 exposed to light to harden the photoresist, and the unexposed portions of.the layer of photoresist dissolved away. A layer of magnesium fluoride may then be evaporated on the exposed portions of the metallic plate 54. In accomplishing this operation it is desirable to maintain the plate at a temperature of the order of 200 C. so as to prevent crazing of the layer 58. The hardened portions of the layer of photoresist may then be burned off leaving a layerof magnesium fluoride on only one side ofthe metallic sheet.54. In the event that it is desired to have a narrow border 57 of exposed metal about theouter periphery of each aperture 56, additional metal may be electroplated within each of the apertures until borders of the desired width are produced. When metal is electroplated within apertures 56 in this manner, their initial diameter should make an allowance for the amount by which it will decrease due to the electroplating operation. 7 e

The shadow mask 32 is disposed adjacent to and coextensive with the storage screen 30 on the side thereof facing the electron guns 14, 16, 18. As shown in Figs. 5 and 6,; the shadow mask 32 has one opening 60 for each set;.of three of the apertures 56 in the storage screen 30. A metal sheet 61 of the order of 0.004" thick composed of an alloyof 70% copper and 30% nickel is a suitable material out of which to fabricate the shadow mask 32. Inthe center, portion of the mask 32 and the screens 28, 30, the openings 60 of the shadow mask 32, the apertures 56 of the storagescreen-30, and the phosphor dots 52 0f the viewing screen 28 are aligned in the manner shown in Fig. 7. In this figure the phosphor dots 52, apertures 56, and the openings 60 are all projectediintoasingle plane and an opening 60 is represented by a shaded circle. Each of the apertures 56 is eentrallydocatedover .a ditferent color phosphor dot. The opening 60, on the other hand, is disposed so that its outer periphery is equidistant from the center of each .of the apertures 56. In the regions nearer the outer periphery ofthe mask 32, on the other hand, allowance .must, of course, be made for parallax of the electron beams. Thus, it is necessary to align the openings 60 of the shadow mask 32 with both the phosphor dots' 52 of the viewing screen 28 and the apertures 56 of the storage screen 30. The spacing between the shadow mask 32 and the storage screen 30 is determined by the spacing between the apertures 56, the distance from the shadow mask 32 to the centers of deflection of the electron beams 20, 22, 24 and the distance separating the centers of deflection of the electron beams.

During the operation of'the device, the cathodes of the electron guns 14, 16, 18 are maintained at a potential of the order of 6000 .volts with respect to the potential of the cathode of the flood gun 42, which may, for example, be maintained at ground. In this case, the shadow mask 32 is maintained at +1000 volts, the metal sheet 54 of the storage screen 32 at +8 volts, and the transparent conductive coating 50 of the viewing screen 28 at 5000 volts positive with respect to ground. The electron beams 20, 22 and 24 are first: directed along the neck portion 12 parallel with each other until they arrive at the centers of deflection 62, 63, 64, respectively, of the yokes 36, 38, as indicated in Fig. 8. Simultaneously with being scanned over, the shadow mask' shown in' Fig.8, the electron beams 20, 22, 24 are converged towards a common point .in the plane .of the mask 32 in the usual manner. The electron beams pass through the openings 60 of the shadow mask 32and impinge'on the storage surface surrounding the apertures 56 directly opposite phosphor dots of the viewing screen 28 of a color corresponding with the signal employed to modulate the electron guns 14, 16, 18. In that. the electron beams 20, 22, 24 would have to traverse both the shadow mask 32 and the storage screen -30 to' impinge on the viewing screen 28, their efliciency to produce light upon reaching screen 28 is less than v of what it would be if the beams 20, 22, 24 were unintercepted. Simultaneously with the beams 20, 22, 24 charging the storage surface surrounding the apertures 56 of storage screen 30, flood electrons provided by the flood gun 42 are directed towards the shadow mask 32. Each opening. 60 in the shadow mask 32 acts as a diverging lens to the flood electrons due to the negative potential gradient from :the mask 32 to the storage screen 30. This lens calculates to be weak and tends to be beneficial in that it improves the uniformity of the flood electrons and,

avoids shadowing of flood electrons by the shadow mask 32. This lens effect is, of course, negligible for the high-velocity beams 20, 22 and '24. The flood electrons which approach the storage surface may be reflected or captured by one of the converging lenses produced in the vicinity of the apertures 56 of the storage screen 30. Flood electrons are thus captured'in proportion to the charge on the surrounding storage surface and are then accelerated through the aperture to the corresponding phosphor dot in alignment therewith to produce a color presentation. If it is desired to produce a half-tone'presentation, the three-color direct-viewing storage tube of the present invention may be operated in the mode defor producing first, second and third electron beams, re-

spectively; means coupled-to each of said electron guns for modulating said electron beams in accordance with colored phosphor dots, the orientation of the first,second and third colored phosphor dots in each of said clusters being dependent on said predetermined relationship; a Storage screen disposed adjacent to and coextensive with said viewing screen on the side thereof nearest said electron guns, said storage screen having a single aperture in alignment with each of said first, second and third colored phosphor dots of said viewing screen; a shadow mask disposed adjacent to and coextensive with said storage screen on the side thereof'nearest said electron guns, said mask having a single opening for each of said clusters of said viewing screen to allow each of said first, second and third electron beams to be incident only. on the storage surface surrounding the respective apertures in alignment with phosphor dots of one of said first, second and third colors; means for producing a negative potential gradient from said shadow mask to said storage screen.means for scanning each of said first, second and third electron beams over saidmask whereby portions of each of said electron beams penetratetherethrough to saidstorage screen to produce a composite charge pattern thereon; and means for directing flood electrons uniformly over the entire area of said shadow mask whereby a portion of said flood electrons penetrate therethrough and are diffused over said storage screen by said negative potential gradient and proceed through respective apertures in said storage screen in proportion to the charge therearound to the phosphor dots of said viewing screen in alignment therewith thereby to produce a color presentation representative of said signals. a

2. The multicolor direct-viewing storage tube as defined in claim 1 wherein said dots are of red, blue and of a picture to be produced.

References Cited in the file of this patent UNITED STATES PATENTS 2,532,339 Schlesinger Dec. 5, 1950 2,659,026 Epstein Nov. 10, 1953 2,685,660 Norga-ard Aug. 3, 1954 2,857,551 Hansen Oct. 21, 1958 

